The subject matter of the present invention relates to a hydraulic safety pin apparatus adapted to be connected between a small diameter tubing and a pressure controlled device in a wellbore for allowing long lengths of the small diameter tubing to be filled with a clean fluid under pressure without also allowing the pressure of the fluid to control or operate the pressure controlled device.
While long lengths of small diameter tubing are used in various downhole applications (such as in connection with operation of safety valves), the bottom of the tubing is normally connected to a device that contains no explosives. As a result, the tubing may be filled with fluid under pressure; and, since the device contains no explosives, one need not be concerned about accidental detonation of the device. However, if a pressure controlled device containing explosives is connected to the bottom of the tubing, when the tubing is filled with fluid under pressure, the pressure of the fluid may accidentally detonate the device. Therefore, an apparatus is needed, which is adapted to be connected between the pressure controlled device and the tubing, for allowing the tubing to be filled with fluid under pressure without simultaneously allowing the pressure of the fluid in the tubing to accidentally detonate or operate the device.
When the device was a tubing conveyed perforating gun having a differential pressure firing head, a prior art mechanical safety pin, connected to the firing head, prevented the firing head from detonating while the perforating gun was assembled at the surface provided that the mechanical safety pin was held firmly in place. A small diameter tubing, connected to the perforating gun, could then be filled safely with water or other fluid. After the small diameter tubing was filled with fluid but prior to detonating the firing head, a drilling rig lifted or removed the firing head from the wellbore so that the mechanical safety pin, connected to the firing head, could be manually removed from the firing head at the rig floor. However, the mechanical safety pin limited the length of the small diameter tubing since the distance along the small diameter tubing, between the firing head and the top of the small diameter tubing, was limited to a length that the drilling rig could lift or pick up in a single lift (usually 90 to 100 feet).